A scientific model is a simplified representation of a real object, process or system. It keeps details relevant to a question and leaves out less useful details. For example, to estimate a toy car’s travel time, we might use its distance and average speed while ignoring its colour. Assuming steady motion makes the calculation simpler, but may limit accuracy if the car frequently stops. Assumptions are deliberate choices, not established facts. A useful model must agree reasonably with observations for its intended purpose. When it does not, scientists check its assumptions and may include additional details.

Science uses carefully defined terms, symbols and standard units so that measurements can be understood and compared everywhere. Mass is measured in kilograms (kg), distance in metres (m), time in seconds (s), and electric current in amperes (A). A quantity’s symbol is not its unit: m can represent mass, while m written after a distance value means metre. Mathematics expresses relationships precisely. For a journey, average speed = total distance/total time, with SI unit m/s. Before calculating, identify the relevant quantities and use consistent units. An equation is a relationship to understand, not merely a rule to memorise.

A scientific law describes a regular pattern in nature, sometimes through an equation. A scientific theory explains patterns using evidence gathered and tested over time; it is not simply a guess. A principle is a broad guiding idea, such as conservation of energy. Laws, theories and models help scientists make reasoned predictions about unfamiliar situations. A prediction becomes scientifically useful when observations or measurements can test it. Agreement increases confidence within the conditions tested, but does not prove an idea correct forever. Disagreement calls for checking measurements, assumptions and explanations rather than ignoring the evidence.

Estimation means finding an approximate value using reasonable assumptions and available information. Begin by understanding the situation, choosing relevant quantities and deciding how precise the answer needs to be. For instance, if a tap delivers about 2 litres each minute, the estimated volume collected in 5 minutes is 10 litres: volume = flow rate × time. This assumes the flow remains roughly steady. The SI unit of volume is the cubic metre (m³), though litres are common in daily life; 1 litre = 0.001 m³. Estimates help detect errors, but tasks requiring precise measurement cannot rely on rough values alone.

Physics, chemistry, biology and earth science organise scientific knowledge, but real situations often connect these branches. Investigating drinking water can involve water flow, dissolved substances and disease-causing organisms. Mathematics helps interpret measurements, while technology applies scientific understanding. Science is also a human activity: people ask questions, develop ideas, share findings and learn from errors. Critical thinking means examining evidence and reasoning before accepting a claim, including one shared widely online. Popularity is not proof. Asking what changed, how it was measured and whether other explanations fit helps us make informed decisions beyond the classroom.